Controlling the air gap of an electric generator as such is generally known. Because of tolerances, inhomogenities, external load conditions and current variations, the rotor of an electric generator can tilt and/or get eccentric. The eccentricity of the rotor can create unwanted effects, such as a decrease of electrical efficiency, and induce large forces on the generator structure, which can have negative effects on components of the generator, in particular on its bearings. Moreover the extreme forces on the generator could cause contact between the rotor and the stator and hence damage to components.
To date, proposals for controlling the air gap deflection are mainly based upon the Wheatstone bridge principle of stator winding arrangement and/or with mechanical stop means. However, the application of the Wheatstone bridge winding is limited to small power motors with the specific application of electrically levitating motor bearings. An example for such an arrangement is disclosed in Khoo, Fittro, Garvey, “An AC selfbearing rotating machine with a single set of windings”, Power Electronics. Machines and Drives. 16-18 April 2002, Conference Publication No. 487, IEE 2002.
However, there is still a need to provide a solution for reducing the rotor eccentricity of a generator, especially for large scale power generators e.g. in applications such as wind turbines.